This is beyond frustrating 
 
Recently found the time an money to upgrade the studio computer (was a Core Duo, DDM2 laptop, now an i5, DDM3). On the old machine, no audio engine dropouts, though it was getting impossible to mix down a recording. I'll note the new machine is a virgin Win7 box, a clean install of Sonar X2 and all other recording software. All updates were made (OS and recording tools). Latest ASIO drivers for the Lexicon Omega.
 
On the new machine, I cannot playback 20 seconds without the %@&^@ audio engine dying.
 
I walked down the long laundry list of possible problems found at http://www.cakewalk.com/Documentation?product=SONAR%20X2&language=3&help=AudioPerformance.23.html#1123645. No success.
 
I also see no common problem source. Sometimes the disc load icon goes red, and sometimes it doesn't.
 
1) How can one isolate the actual cause of the audio engine dropout?
 
2) Aside from the list of potential causes on the aforementioned web page, what else might be causing a relatively robust machine to choke on a 10 track mix playback?

Download Latency Monitor and see what processes are taking too much time.
http://www.resplendence.com/latencymon

Here is a good thread about interpreting results from Latency Monitor.
http://forum.cakewalk.com/FindPost/3205730

You saying you worked through the list. Did you change any settings? Latency? Did you set your sound card as master for clock- for recording and playback? Did you disable your onboard sound card? (In system- set your Lexicon as default). What about the Antivirus? Check all the cables?

Microapp, many thanks. Quite an interesting tool. And vladasyn, yes I made changes and backed them out, testing everything that could.
 
So, things are better though LatencyMon still reports a borderline situation. Being an ex-mini mainframe fellow, I only dive into Windows innards when necessary, so I have a bit of a learning curve. Thanks to for the page to interpret LatencyMon, though I did not locate a concise description ... I'll have to dig through the thread some more.
 
The embarrasing admission is that I had notice noticed the "See Other" section of the Windows performance screen in Control Panel, where Microsoft had hidden the "Maximum Performance" option (why is it whenever MSFT tries to be slick, they make things for obtuse and difficult?). So, switching that over at least stopped massive dropouts.
 
LatencyMon reports the max latency was 21204 ms from USBPORT.SYS. This makes sense give the Lexicon Omega is the audio device in use. But in the driver page, USBPORT has a "highest execution time" of 0.33 ms, so I don't understand the main/driver divergence. The other red-zone element is the hard pagefault resolution time (14239 ms), and that was in an SVCHOST instance. I may play with buffers again now that the dropouts are somewhat tamed.
 
One problem I may have is finding the documentation for tuning the BIOS (AMI ver 0502) which I have yet to locate on the net -- anyone know where to grab the docs? Lots of options in the BIOS, few of which are above my paygrade.
 
Some other stats:
 
MEASURED INTERRUPT TO USER PROCESS LATENCIES
Highest measured interrupt to process latency (µs): 21204.283224
Average measured interrupt to process latency (µs): 6.084515 (assume not terrible?)
Highest measured interrupt to DPC latency (µs): 208.958061
Average measured interrupt to DPC latency (µs): 0.937431 (assume not terrible?)
 
DPC count (execution time <250 µs): 1437037
DPC count (execution time 250-500 µs): 0
DPC count (execution time 500-999 µs): 12
DPC count (execution time 1000-1999 µs): 0
DPC count (execution time 2000-3999 µs): 0
DPC count (execution time >=4000 µs): 0

If you're running wifi networking, if you've not already tried it, go into Windows Control Panel/Device Manager.

Find the wifi adaptor in the list, right click on it and disable it (not uninstall, just disable).

Then try running the latency monitor again and see if things have improved. It's not always the case, but a primary cause of high PCI bus latency problems is wifi adaptor drivers that hog resources for too long. Omce the time they've hogged exceeds the ASIO audio buffer you get popping and droputs in the audio. It's not uncommon to have to disable the wifi adaptor while working in the DAW then enable it again if you need it omce you've finished.

Wired ethernet hardly ever seems to cause any problems, so if wifi is causing younproblems and you want continual networking, ethernet is probably the way to go.

After that, if problems persist I'd suggest looking at Windows power settings as the next step. Set everything to 100% and disable USB port suspension by Windows, otherwise things attached by USB tend to get put to sleep. USB power suspend also needs doing in Device Manager by right-clicking the USB ports as well - the power settings don't over-ride device manager for some reason lnown only to MS.

After that, disabling cpu core parking and, if necessary, tweaking BIOS cpu power and sleep settings are often worth investigating.

PCs are put together and by default configured for the "avaerage user". The average user, even game players, doesn't notice if the PC takes 10 or 15 milliseconds to fire up a cpu core or speed one up, or if there's a 20ms wait while something in the background has 100% of Window's attention. DAW users after as close as possible to real-time audio don't make average demands on the PC, for us it matters.

What are the full specs of your Daw? This should be in your signature so we all can see it without asking you each time you may need assistance. 
 
See other peoples signature to get an idea.

Unfortunately all motherboards do not interact with Win power settings the same way.
If your bios has some CPU clock mgmt option, disable it. Used to be called Intel Speed Step.
On my ASUS mb, I leave turbo mode enabled and in Win, set min processor to 100%.
On this mb anyway, that leaves the CPU clock static and at the turbo speed.
This scheme has worked on a couple of Intel mb's and my current ASUS mb.
+1 to tlb's suggestions especially re: WIFI.
Also at least until you ID the issue, disconnect any unnecessary USB devices.
 
Some PC's will benefit from disabling internal onboard audio devices . Some video cards have HDM! audio devices and I would disable those as well. At least for troubleshooting.
If you have disk issues, go into devices manager and make certain your disk is using DMA mode.
https://www.ifixit.com/Wiki/Enabling_DMA_Mode_Transfers
 
Are you sure all cores are enabled. Some bios have a single core setting.  Do you see activity in Sonar Performance Monitor for more than the first core ?
 
Not sure you will find  bios specific details above what is in your mb manual. What is you mb exactly ?
 

TLW, thanks. No wi-fi, no parked CPUs, all power settings at 100%.
 
Jesse G, thanks for the protocol suggestion. I'll see if I can assemble enough data.
 
============
 
Sonar X2 producer, Windows 7 64-bit, i5 650 @ 3.2GHz, 8GB DDR3 @ 1333MHz, Intel HD Graphics, 
Lexicon Omega using ASIO driver, M-Audio Trigger Finger

This is a pretty common problem. It is easy to think that a new powerful system will solve all of your problems, but it is rare that all of the parts and pieces work together to make a trouble-free DAW. This is one of the many reasons why custom DAW builders still exist.
 
For what it is worth, try to keep the Lexicon on its very own USB bus and not shared with your mouse and keyboard, or any other USB device. You'll have to do some research to discover which USB ports connect to which bus internally. Also, if the Lexicon is a USB2 device, make sure it is only plugged into a USB2 port. Most new motherboards offer USB3 ports and many USB2 audio interfaces have trouble with them.
 
Regards,
Dan